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Chapter 1
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Chapter 1
Chapter 1
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Pair of Elements
To compel a body to move in a definite path, it must be paired with another , the shape of which is determined by the nature of the relative motion of two bodies.
Mechanism
Combination of rigid bodies so arranged that the motion of one compels the motion of others, according to a law depending on the nature of combination.
Machine
A combination of resistant bodies so arranged that by their means the mechanical forces of nature can be compelled to produce some effect or work accompanied with certain determinate motions.
Constructive Mechanism
Calculates the forces acting on different parts of the machine, selects materials for strength and durability, considers repair and manufacturability
Incomplete Pair
Formed when the reciprocal restraint of two elements is complete; that is, that each of the two bodies, by the rigidity of its material and the form given to it, restrained the other.
Pure Mechanism or Kinematics of Machines
Treats the motion and forms of the parts of a machine and how they are supported and guided, independent of their strength
Rigid Body
Body whose component particles remain at a constant distance from one another
Frame
Structure that supports moving parts and regulates their motion in a machine
Structure
A combination of resistant bodies capable of transmitting forces or carrying loads but having relative motion between parts.
Closed or Lower Pair
If one element not only forms the envelope of the other, but also encloses it, the forms of the elements being geometrically identical, the one being solid or full, and the other being hallow or open
Inversion of Pairs
The absolute motion of the moving piece is the same, whichever piece is fixed.
Particle
Infinitesimal part of a body represented by a point
Modes of Transmission
If the action of natural forces of attraction and repulsion is not considered, one piece cannot move another unless the two are in contact or are connected to each other by some intervening body that is capable of communicating the motion by the one to the other.
Follower
Piece of a mechanism whose motion is effected
Science of Mechanism
The laws governing the motion of the parts of a machine and the forces transmitted by these parts
Driver
Piece of a mechanism that causes motion
Higher Pair
Formed when the elements are in point or line contact and do not enclose each other.
Bearings
Surfaces of contact between two pieces with relative motion
Stationary bearing
Bearing where one piece is stationary
Moving bearing
Bearing where both pieces are moving
Collars
It is very often required that pulleys or wheels turn freely on their cylindrical shafts and at the same time have no motion along them
Keys
Sometimes pulleys or couplings must be free to slide along their shafts but at the same time must turn with them, they must then be changed to a sliding pair
Crank
An arm rotating or oscillating about an axis
Lever
The combination particularly when the motion is oscillating over a relatively small angle
Action of a Crank
A crank may be considered as a rigid piece connecting one member of a pair of cylindrical elements to one member of another pair
Link
A rigid piece or a non elastic substance which serves to transmit force from one piece to another or to cause or control motion
Linkage
It consists of a number of pairs of elements connected by links
Four bar Linkage
A mechanism consisting of two cranks and two connecting rods connected to each other by a rigid rod or bar called the connecting rod coupler or floating link
Untitled Flashcards
Study
223 Centripetal Force
The force that keeps an object moving in a circular path. It is directed towards the center of the circle and is responsible for constantly changing the direction of motion.
216 Angular Speed
The time rate of turning of a body about an axis or the rate at which a line on a revolving body is changing direction and is expressed in angular units per unit of time.
217 Uniform and Variable Speed
Speed is uniform when equal spaces are passed over in equal times, however small the intervals into which the time is divided. Speed is variable when unequal spaces are passed over in equal intervals of time.
218 Velocity
A word often used synonymously with speed, but it includes direction and sense as well as speed. The linear velocity of a point is not fully defined unless the direction and sense in which it is moving and the rate at which it is moving are known.
219 Linear Acceleration
The time rate of change of linear velocity. Acceleration may involve a change in speed or direction or both. Acceleration may be either positive or negative.
220 Angular Acceleration
The time rate of change of angular velocity. Angular acceleration can involve a change in either speed or direction of rotation or both.
221 Translation
Motion of a body when all its component particles have the same velocity as regards both speed and direction. It can be either rectilinear or curvilinear.
222 Turning Bodies
All motion consists of translation, turning about an axis, or a combination of the two. Turning bodies refer to objects that are rotating about an axis.
